Electric heating mat



Oct. 25, 1966 D. M. CHAPMAN, JR 3,281,578

ELECTRIC HEATING MAT Filed NOV. 21, 1963 5g g DNALD M. cHAPMAN,Jr.

BY We M,mw 7" s/fb United States Patent O 3,281,578 ELECTRIC HEATING MAT Donald M. Chapman, Jr., Plainville, Conn., assignor to The Smith-Gates Corporation, Farmington, Conn., a corporation of Connecticut Filed Nov. 21, 1963` Ser. No. 325,339 14 Claims. (Cl. 219-528) This invention relates to electric heating mats, and deals more particularly with such a mat especially adapted for use in melting or preventing the accumulation of ice and snow on sidewalks and other exposed areas. It also relates to a method for making such a mat.

The general object of this invention is to provide a snow and ice melting mat of the foregoing character which mat is of light weight, ilexible and is otherwise of such a character as to be portable and readily placed on and taken up from a given area of use, as well as being easily folded or rolled into a compact bundle for storage.

Another object of ythis invention is to provide an electric heating mat of the foregoing character which heating mat is directional insofar as a substantially greater portion of the heat produced thereby is emitted from one side thereof as compared to the other side, thereby giving the mat a relatively hot side and a relatively cool side, In keeping with this object, a further object is to provide a directional heating mat having relatively hot and cool sides and which may be placed on a given area with its hot side down to melt previ-ous accumulations of ice or snow with its hot side up to melt snow as it falls and to prevent the formation of ice.

A- further object of this invention is to provide a mat of the foregoing character which is of durable construction and which may be walked on without injury to the mat and particularly without chaiing of the heating elements.

A still further object of the invention is to provide a convenient and low cost method of making a heating mat of the foregoing character.

Other objects and advantages of the invention will be apparent from the following description and from the drawing forming a part hereof.

The drawing shows preferred embodiments of the invention and such embodiments will be described, but it Will be understood that various changes may be made from the constructions disclosed, and that the drawing and description are not to be construed as denng or limiting the scope of the invention, the claims forming a part of this specication being relied upon for that purpose.

Of the drawing:

FIG. 1 is a top view of a heating mat embodying the present invention with a portion of the top cover sheet bei@ broken away to illustrate the arrangement of the heating wire and other elements contained inside the mat;

FIG. 2 is an enlarged fragmentary sectional View taken on line 2 2 of FIG. 1;

FIG. 3 is a fragmentary vertical sectional view showing a method of heat sealing the various sheets of plastic material making up the mat of FIG. l;

FIG. 4 is a fragmentary top view showing the mat of FIG. 1 at one point in its manufacture; and

FIG. 5 is an enlarged sectional view similar to FIG.

ice

2 but showing an alternative embodiment of the invention.

Turning now to the drawing and rst considering FIGS. 1 and 2, a mat embodying the present invention is shown generally at 10 and comprises two relatively thin cover sheets 12 and 14, a relatively thicker sheet 16 and an intermediate thin sheet 18. Each of the sheets 12, 14, 16 and 18 is of substantially the same `size and shape as viewed looking toward one of the two major surfaces of the -rnat as in FIG. 1, but it will be understood that such size and shape may be varied considerably without departing from the invention. The -three thin sheets 12, 14- and 18 are made of a water impervious material and the two cover sheets 12 and 14 are additionally preferably made of such a material as to have a high wearresistant characteristic. The thicker sheet 16 preferably provides both resiliency and heat insulation and preferably consists of a foamed or cellular plastic material. Although various different materials may be used for the sheets 12, 14, 16 and 18, the material or materials selected should be compatible as regards heat sealing so that the sheets may be heat sealed one to another in the manner hereinafter described. More particularly, the sheets 12, 14, 16 and 18 are all made out of or contain a thermoplastic material and preferably the thin sheets 12, 14 and 18 have substantially t-he same melt index while the foamed or plastic sheet 16 has a melt index no greater than that of the other sheets. As used herein, the term melt index means the temperature at which the material in question is rendered sufliciently fluid or melted to eect heat sealing. As an example of suitable materials for the various sheets making up the mat 10, the cover sheets 12 and 14 may be made from a vinyl plastic reinforced with a nylon fabric, the intermediate Sheet 18 may be a vinyl plastic without any reinforcement and the thicker heat insulating sheet 16 may be made of foamed polyurethane.

The sheets 12, 14, 16 and 18 are sealed to one another, as shown best in FIG. l, along elongated seal zones 20, 20 which are arranged in spaced parallel relationship to one another and, in the illustrated example, extend parallel to the width of the mat. The exact nature of the seal effected at each of the seal zones 20, 20 may vary widely without departing from the invention and in the illustrated case the act-ual seal is located along a narrow oval-shaped line or band 21 .as shown. The mat is also sealed along its peripheral edges, there being two longitudinal edge seal zones 22, 22 and two transverse edge seal zones 24, 24 as shown. Along each of the edge seal zones 22, 22 and 24, 24 the two cover sheets 12 and 14 are bonded directly to each other or to the intermediate sheet 18 to provide a moisture proof seal preventing the entrance of water into the mat. Each elongated seal zone 20 at each of its ends terminates short of the adjacent longitudinal edge seal zone 22 to allow the heating wire to pass between adjacent pockets as hereinafter described.

Referring to FIG. 2, it will be noted that at each elongated seal zone 20 the top cover sheet 12 is bonded or sealed to the intermediate sheet 18 along the seal line 21 and that the cellular sheet 16 is likewise bonded to the intermediate sheet 18 and to the cover sheet 14 in the area of the seal line. Although the illustrated type of heat seal is preferred, the seal could also be made in such a manner as to apply sutlicient heat to melt away 3 the cellular material of the sheet 16 at the seal line during the sealing process and to bond the lower cover sheet 14 directly to the intermediate sheet 18, thereby integrally joining the three thin sheets 12, 14 and 18.

From the foregoing description of the elongated seal zones 20, 20, and of the nature of the seal at each of the said Zones, it will be noted that the two sheets 12 and 18 are formed into a series of pockets 28, 28 each located between two adjacent seal zones 20, 20. Each pocket 28 therefore has an inner surface made up of part of the inner surface of the sheet 12 and part of the adjacent lsurface of the sheet 18. A length of heating wire 30 is contained between the two sheets 12 and 18 and is formed into a plurality of loops 32, 32 each of which is 'loosely received in an associated one of the pockets 28, 28. By loosely received it is meant that each loop is not stitched, sealed or otherwise attached to either of the two sheets 12 or 18 or to any other support and is held in place solely by engagement with the sheets and with a spacing means located between the two arms of the loop. The arrangement of the heating wire loops 32, 32 in the pockets 28, 28 may be varied widely, for example each pocket could contain one loop extending the full length thereof, but the preferred arrangement is shown wherein each pocket 28 contains two loops each extending into the pocket from a respective one of its ends and terminating short of a line 34 passing longitudinally of the mat through the transverse middle thereof perpendicular to the seal Zones 20, 20. As a result of this arrangement, the heating wire 30 crosses the center line 34 only at the longitudinal ends of the mat and therefore the mat may be readily folded along the line 34 with little resistance from the wire. As shown in FIG. l, the wire 30 forms a closed path in passing through the mat and has both of its ends located at one end thereof and joined to a power supply cord 36 by a suitable electrical connection 38.

The placement of the loops 32, 32 in the pockets 28, 28 is such that each arm 40, 40 of each loop extends along a respective one of the sides of the associated pocket 28. The arms 40, 40 of the various loops are in turn maintained in this relationship in the pockets 28, 28 by a plurality of spacers 42, 42 made of electrical insulating material, one spacer 42 being inserted in each of the pockets 28, 28. The spacers may be made of various different materials, corrugated cardboard being the presently preferred material.

The heating wire 30 used in the mat 10 may be of various different constructions and may, for example, be similar to the heating element shown and described in more detail in my copending application Serial No. 238,927, filed November 20, 1962 and entitled Heating Mat. The arrangement of the heating wire and the use of the spacers 42, 42 causes the heat generated to be relatively evenly distributed over the area of the mat and the use of the spacers 42, 42 prevents portions of the wire from chafing against one another in use.

The sheet 16 of heat insulating material in the mat 10 provides the mat with a directional effect whereby a relatively greater amount of heat is emitted from one side thereof (the side of the cover sheet 12) than is emitted from the other side (the side of the cover sheet 14). The mat therefore may be placed on a given area with its hotter side facing in the direction in which a greater amount of heat may be desired. For example, if the mat is to be used to melt previous accumulations of ice or snow, the mat may be placed with the hot side facing downwardly against the ice -or snow. Alternatively, if the matr is to be used to melt snow or sleet as it falls, or to prevent the accumulation of ice, it may be placed on the area to be protected with the hotter side facing up. In this regard, it should be noted that preferably the two cover sheets 12 and 14 are differently colored or otherwise marked so that the user may readily distinguish the hotter from the cooler side.

The use of rugged wear-resistant material, such as nylon reinforced vinyl plastic, for the cover sheets 12 and 14 permits the mat to be repeatedly stepped on or walked over without injury thereto and the use of the cellular insulating sheet 16, which is resilient in nature, has the added benefit of giving the mat a satisfactory feel when so walked on. That is, in walking over the mat, a person will not normally feel the loops of the heating wire due to the fact that the wire will be pressed into or cushioned by the sheet 16. Furthermore, the sheets 12, 14, 16 and 18 are all quite fiexible so that the mat in addition to being capable of being readily folded along the longitudinal center line 34 may also be folded or rolled in the transverse direction to form a compact bundle for convenience in storing or shipping the mat.

Considering now the manufacture of the mat 10, the first step in the preferred method of assembly is to provide a lay-up of plastic sheets arranged in the desired order and to then heat seal the sheets along the elongated seal zones 20, 20 to unite the sheets into a single unit and to form the pockets 28, 28. The heat sealing may be performed in various different ways, but preferably it is performed by dielectric heating as shown in FIG. 3. Referring to this figure, the lay-up of sheets is indicated generally at 44 and consists of initially separate sheets 12, 14, 16 and 18 which ultimately become the sheets 12, 14, 16 and 18 respectively of the finished mat 10 shown in FIGS. l and 2. This lay-up is placed between a bottom electrode 46 and a top electrode 48 of a dielectric heating device with the sheets 12 and 18 facing the top electrode 48 and the sheet 14 facing the bottom electrode. The bottom electrode 46 has a fiat upper surface which engages the cover sheet 14 and the upper electrode 48 is shaped so as to have a downwardly facing surface 50 having an elongated oval shape similar to each of the finished seal lines 21, 21 of FIG. 1. The area of the top electrode 48 which engages the cover sheet 12 is therefore substantially smaller than the area of the bottom electrode 46 which engages the cover sheet 14. In effecting the seal, the top electrode 48 is moved downwardly toward the bottom electrode 46 to compress the lay-up between the electrodes as shown in FIG. 3, and while the lay-up is so compressed, a high frequency alternating potential is produced between the two electrodes so as to produce an alternating electric field pas-sing through the lay-up which causes the material of the various sheets to be heated to or beyond their melt index at which point the sheets bond to one another. It will also be evident from FIG. 3 that because of the smaller area of the top electrode 48 the electric field passing through the two sheets 12 and 18 will be of greater intensity than the field passing through the lsheets 16 and 14 and therefore a relatively firmer seal is obtained between the two sheets 12 and 18 than is obtained between the sheet 18 and the sheet 16 and between the sheet 16 and the sheet 14. This firm seal between the sheets 12 and 18 is desirable insofar as it reduces the possibility of the sheets 12 and 18 coming apart at their seals and thereby allowing the heating wire to move out of the pockets.

After lche lay-up 44 is sealed .along the desi-red number of elongated seal zones 20, 20, the heating wire 30 is inserted intro the various pockets 28, 28 as by forming the wire sequentially into a number of loops and pushing each loop into an associated pocket 'by a tool 52 as `shown in FIG. 4. After all of the pockets have been filled w-ith loops of heating wire, the ends of the heating wire are joined to a power cord 36 by the connection shown at 38 in FIG. 1 and thereafter the edges of the mat are sealed as at 22, 22 and 24, 24 and around the power cord 36 to produce the finished mat.

FIG. 5 shows an alternative construction of the invention in which the intermediate sheet 18 is eliminated. Referring to FIG. 5, the mat therein shown -is indicated gener-ally at 'S2 and comprises two cover sheets 54 and 56 and a sheet of cellular heat insulating material 58. The two cover sheets 54 and 56 .are sealed to one another along elongated seal zones 60, 60, similar to the seal zones 20, 2t) of FIG. 1, and the nature of the seal at each such seal zone is such that along each seal line the cellular sheet 58 is melted away and the top cover sheet 54 bonded directly to the bottom cover sheet 56, the cover sheets therefore being firmly joined to provide pockets for receiving the loops of heating wire, suc-h heating wire being shown at 62. Instead of completely melting away the material of the cel-lular sheet 58, the top sheet 54 could be heat sealed to the sheet 53 at the seal zone. Also as shown in FIG. 5, the elimination of the intermediate sheet 18 also permits the elimination of spacers in the pockets to maintain the loops of wire in a separated condition. That is, in each pocket the top sheet holds the heating wire 62 against the cellular sheet 5-8 so that the material of the cellular sheet .is displace-d and takes on the shape sh-own so that a quantity of the material is located between the two arms of the heating wire loop to thereby serve as a spacing means fulfilling the function of the spacers 42, 42 of the FIG. l and 2 construction. It will be understood, however, that separate spacers may be used in the FIG. 5 construction, if desired.

The invention claimed is:

1. An electric heating mat comprising two layers of superimposed plastic sheet material sealed to each other along a plurality of elongated seal zones arranged in parallel spaced relation to each other so as to form said layers of sheet material into a plurality of pockets each located between tw-o adjacent seal zones and each hav-ing an inner surface comprised of parts of the adjacent surfaces of said two layers of plastic sheet material, an elongated heating wire loosely received between said two layers of sheet material and arranged in a plurality of loops with each loop being received in an associated one of said pockets and having one arm thereof extending along one side of the associated pocket and the other arm thereof extending .along the other side of said pocket, and a spacing means located between and engageable with the two arms of each loop for maintain-ing the spaced relat-ionship of said two arms.

2. An electric heating mat as defined in claim 1 further characterized by said spacing means comprising a plurality of elongated spacers each of which is an element separate from said two sheets and is received in a respective one of said pockets between the arms of the loop of heating wire therein so as to maintain said arms separated from each other.

3. An electric heating mat as defined in claim 1 further characterized by said sheets being rectangular in shape and additionally sealed to each other along seal zones extending along and adjacent their edges, said elonagted seal zones extending parallel to one pair of said edges of said sheets and each such elongated seal zone at each of its ends terminating short of the adjacent edge seal Zone so as to provide communication between adjacent pockets, and each of said pockets receiving two of said loops of heat-ing wire with one of said loops extending into the pocket from one end thereof and the other loop extending into the pocket from the other end thereof,

4. An electric heating mat as defined in claim 3 further characterized -by each of said loops of heating wire extending into its associated pocket by such a distance that its laterally inner end is disposed short of a line extending perpendicular to said elongated seal zones wit-h the res-ult that said mat may be folded along said line with little resistance from said wire.

5. An electric heating mat as defined in claim 1 further characterized by one of said layers of superimposed plastic sheet material having an outer surface of said mat and the other of said layers comprising a sheet of foamed plastic.

6. An electric heating mat as defined in claim 5 further characterized by said spacing means comprising a quantity of the material of said sheet of foamed plastic l0- cated between the two arms of each loop.

7. A-n electric heating rnat comprising two superimposed relatively thin plastic cover sheets the outer surfaces of which provide the outer surfaces of said mat, said two thin sheets being separated by a relatively thick sheet of cellular plastic heat insulating material with one of said cover sheets being sealed to one of the other of said sheets along a plurality of elongated seal zones arranged in parallel spaced relation to each other so 'as to form a plurality of pockets between sa-id one cover sheet and said sheet of cellular plastic material, each of said pockets being located between two adjacent seal zones and each having an inner surface comprised off part-s of the adjacent surfaces of said one cover sheet .and said sheet of cellular plastic materia-l, and `an elongated heating wire received between said one cover sheet and said sheet of cellular plastic material and arranged in a plurality of loops with each loop being received in an associated one of said pockets and having one arm thereof extending along one side of the associated pocket and the other arm thereof extending along the other side of said pocket.

8. An electric heating mat as defined in claim 7 further characterized by a plurality of elongated spacers each of which is an element separate from said plastic sheets and is received in a respective one of said pockets between the arms of the loop of heating wire therein so as to maintain said arms separated Vfrom each other.

9. An electric heating mat as defined in claim 7 further characterized by each of said cover sheets comprising nylon fabric embedded in a thermoplastic plastic material.

10. An electric heating mat as defined in claim 9 further characterized by said cellular plastic material having a melt index no higher than the melt index of said thermopla-stic plastic material of said cover sheets, .an-d said two cover sheets being bonded to each other at said elongated seal zones.

11. An electric heating mat comprising two relatively thin superimposed plastic cover sheets separated by a relatively thicker sheet of cellular plastic heat insulating material and another relatively t-hin intermediate sheet of plastic material, one of said cover sheets being sealed to said intermediate sheet along a plurality of elongated seal zones arranged in parallel spaced relation to each other so as to form a plurality of pockets between said one cover sheet yand said intermediate sheet, each located between two adjacent seal zones and each having an inner surface comprised of parts of the adjacent surfaces of said one cover sheet and said intermediate sheet, an elongated heating wire received between said one cover sheet and said intermediate sheet and arranged in a plurality of loops with each loop being received in an associated one of lsaid pockets and having one arm thereof extend-ing along one side of t-he associated pocket and the other `arm thereof extending along the other side of said pocket, and a spacing means locate-d between and engageable with the two arms of each loop for maintaining the spaced relationship of said two arms.

12. An electric heating mat as defined in claim 11 further characterized by said sheet of cellular plastic material being sealed to -said intermediate sheet and to the other of said cover sheets at said elongated seal zones.

13. An electric heating mat as defined in claim 11 further characterized lby each of said cover sheets comprising nylon fabric embedded in a thermoplastic plastic material and said intermediate sheet comprising a sheet of unreinforced thermoplastic plastic material.

14. An electric 'heating mat as defined in claim 11 further characterized by each of said cover sheets comprising a sheet of vinyl plastic reinforced with a nylon fabric, said intermediate sheet comprising a sheet of unireinforced vinyl plastic, and said sheet of cellular material comprising a sheet of foamed polyurethane.

(References on following page) 7 8 References Cited by the Examiner 2,985,742 5 1961 Rea 219--529 I D T PATENTS 2,990,607 7/'196'1 Ne-gromanti 29-155.5 UN TE STA ES 3,041,441 6/ 19612 Elbert et a1. 219-345 Charles X 3 Owens X 1,376,987 5/1921 Wirt 219-212 X 5 1,994,759 3/ 1935 Dermott 219-528 FOREIGN PATENTS 2,741,692 4/1956 `Luke 219-528 747,511 4/1956 Great Brit-ain. 2,834,862 5/11958 Meyers 219-345 2,844,696 7/ 1958 Custer 219-228 X RICHARD M. WOOD, Primary Examiner. 2,873,352 2/ 1959 Franco 219-228 2,942,330 6/1960 Luke M1555 10 V. Y. MAYEWSKY, Asszsfant Exammer.

2,948,802 l8/1960 Shaw 219-212 

1. AN ELECTRIC HEATING MAT COMPRISING TWO LAYERS OF SUPERIMPOSED PLASTIC SHEET MATERIAL SEALED TO EACH OTHER ALONG A PLURALITY OF ELONGATED SEAL ZONES ARRANGED IN PARALLEL SPACED RELATION TO EACH OTHER SO AS TO FORM SAID LAYERS OF SHEET MATERIAL INTO A PLURALITY OF POCKETS EACH LOCATED BETWEEN TWO ADJACENT SEAL ZONES AND EACH HAVING AN INNER SURFACE COMPRISED OF PARTS OF THE ADJACENT SURFACES OF SAID TWO LAYERS OF PLASTIC SHEET MATERIAL, AN ELONGATED HEATING WIRE LOOSELY RECEIVED BETWEEN SAID TWO LAYERS OF SHEET MATERIAL AND ARRANGED IN A PLURALITY OF LOOPS WITH EACH LOOP BEING RECEIVED IN AN ASSOCIATED ONE OF SAID POCKETS AND HAVING ONE ARM THEREOF EXTENDING ALONG ONE SIDE OF THE ASSOCIATED POCKET AND THE OTHER ARM THEREOF EXTENDING ALONG THE OTHER SIDE OF SAID POCKET, AND A SPACING MEANS LOCATED BETWEEN AND ENGAGEABLE WITH THE TWO ARMS OF EACH LOOP FOR MAINTAINING THE SPACED RELATIONSHIP OF SAID TWO ARMS. 